lowndrul lowndrul - 1 month ago 14
LaTeX Question

Trimming extra horizontal rule in LaTeX tables from R's xtable

Q: How can I trim the extra horizontal rule length in LaTeX tables from R's

xtable
?

I'd like to do something like you see in my R code below. But that code throws and error, not producing the desired result.

% table 1
\begin{table}[ht]
\centering
\begin{tabular}{@{}lrr@{}}
\toprule
& a\_a & b\_b \\
\midrule
A & 0.35 & -1.05 \\
B & 0.64 & 0.92 \\
\bottomrule
\end{tabular}
\end{table}

% table 2
\begin{table}[ht]
\centering
\begin{tabular}{lrr}
\toprule
& a\_a & b\_b \\
\midrule
A & 0.36 & -1.05 \\
B & 0.64 & 0.92 \\
\bottomrule
\end{tabular}
\end{table}


tables

# Begin R code
library(xtable)
library(stringr)
options(xtable.comment = FALSE)
set.seed(10)
mat <- matrix(rnorm(4), nrow=2)
rownames(mat) <- LETTERS[1:2]
colnames(mat) <- str_c(letters[1:2], "_", letters[1:2])
#mat.x <- xtable(mat, caption="My Caption!", align="lrr", digits=2) # No Error!
mat.x <- xtable(mat, align="@{}lrr@{}", digits=2) # Error!
print(mat.x,
sanitize.text.function = function(x){x},
sanitize.colnames.function = function(x){str_replace_all(x, "_", "\\\\_")},
floating=T,
hline.after=NULL,
math.style.negative=F,
add.to.row=list(pos=list(-1,0,nrow(mat.x)),
command=c("\\toprule ", "\\midrule ", "\\bottomrule ")))

# Error in `align<-.xtable`(`*tmp*`, value = "@{}lrr@{}") :
# "align" must have length equal to 3 ( ncol(x) + 1 )
# In addition: Warning message:
# In .alignStringToVector(value) : Nonstandard alignments in align string

Answer

You need to pass either a string with the same number of characters as the number of columns + 1, or a string of this length. So try (amongst other permutations)

align=c("@{}l", "r", "r@{}")

To see why have a look at the functions.

library(xtable)

set.seed(10)
mat <- matrix(rnorm(4), nrow=2)
rownames(mat) <- LETTERS[1:2]
colnames(mat) <- paste0(letters[1:2], "_", letters[1:2])
xtable(mat, align="@{}lrr@{}", digits=2) 

"align" must have length equal to 3 ( ncol(x) + 1 )

The warning suggests passing a vector of length three, so try

xtable(mat, align=c("@{}l","r", "r@{}"), digits=2)
# \begin{table}[ht]
# \centering
# \begin{tabular}{@{}lrr@{}}
# ---
# ---

So that works as expected. Also the align argument is robust to how you pass the string, as long as it is of the required length.

xtable(mat, align=c("@{}lrr@", "{", "}"), digits=2)
# \begin{table}[ht]
# \centering
# \begin{tabular}{@{}lrr@{}}
# ---
# ---

To see why the first string didn't work look at the relevant parts of xtable:::xtable.data.frame function: must be to do with align

align(x) <- switch(1 + is.null(align), align, c("r", c("r", "l")[(characters | factors) + 1]))

This leads to xtable:::`align<-.xtable, and then xtable:::.alignStringToVector